Known in the art is the prosthetic hip joint Gilibertya P. shaped as a metallic pin inserted into the medullary canal of the femur, a metallic spherical head connected to the pin and introduced into the cotyloid cavity, and a cup-shaped metallic sphere insertable into the cotyloid cavity, i.e., such a sphere that is in contact with the head of the prosthetic hip joint in the course of its functioning (U.S. Pat. No. 3,982,281).
In such an endoprosthesis its pin has a cross-sectional area, which gradually diminishes towards the pin bottom end so that the maximum pin width is less than the diameter of the medullary canal throughout the entire pin length. That is why such a hip joint prosthesis is installed with the aid of additional fixing. Such fixation is carried out with the use of curable osseous cements. To this end after having removed, for a required depth, the spongy layer and the bone marrow, a liquid noncured composition of osseous cement is injected into the thus-formed hollow space, whereupon the pin of an endoprosthesis is inserted into said space.
However, such a construction of the endoprosthesis under consideration fails to provide its reliable fixing in the medullary canal, which is due to low adhesion between the skin surface and the osseous cement, as well as to a wide difference between the elasticity modulus of the material of the endoprosthesis pin and that of the osseous cement and the femoral bone itself.
All the above-stated results, under permanent cyclic load, in loosening of the endoprosthesis and resorption of the bone surfaces. According to recent evidence, 80 percent of such endoprostheses are to be removed after 5 to 7 years of functioning.
Known in the art is the endoprosthesis Niederer (U.S. Pat. No. 4,430,76) which is also shaped as a metallic pin adapted to be introduced into the femoral medullary canal, and a head insertable into the cotyloid cavity. The pin of the prosthesis in question is made as two components arranged at an angle to each other whose plain flat surfaces are provided with a plurality of shallow additional parallel grooves arranged lengthwise of the pin. Such an endoprosthesis is also installed with the use of osseous cements, so that said grooves are filled with the cement. Provision of such grooves adds to the adhesion between the cement and the pin and makes fixation of the prosthesis more reliable. However, even with such construction of the endoprosthesis too great a difference between the elasticity moduli of the cement and pin and permanent cyclic load applied to the hip joint endoprosthesis result in loosening of the latter in the medullary canal, so that the percentage of the prosthesis removed in 5 to 7 years is the same as in the endoprosthesis construction discussed hereinabove.
Known in the present state of the art is an artificial hip joint of the Sivash system, incorporating a metallic cotyloid cavity and an articulated device aimed at substitution of the femoral head. The pin of the endoprosthesis is fashioned as a shaped solid metallic rod, which is tightly inserted into the preliminarily enlarged medullary canal without any additional fixing (cf. `Operative orthopedics` by Movshovich, 1983, Meditsina Publishers, Moscow, pp. 203-207 (in Russian)).
Installation of the aforementioned endoprosthesis should necessarily be preceded by enlargement (by drilling-out) of the medullary canal so as to provide exact correspondence of the latter to the diameter of the rod of the prosthetic joint, which inflicts additional operative injury on the patient operated upon. It is due to tight fixing of the endoprosthesis that its pin exerts permanent impact on the surface of the bone tissue, thus causing resorption of the latter and loosening of the endoprosthesis.
One more prior-art construction of an artificial hip joint is known to comprise a pin insertable into the bone marrow of the femur and a head to be introduced in the cotyloid cavity (cf. `Operative orthopedics` by I. A. Movshovich, 1983, Meditsina Publishers, Moscow, pp. 216-217 (in Russian). When applied the pin of the prosthesis is tightly introduced into the preliminarily enlarged medullary canal and is additionally fixed with the aid of osseous cement. However, use of the prostheses of the character set forth hereinabove results in resorption of the bone tissue at the place of its contact with the metal of the pin. Employment of osseous cement to some extent diminishes such an adverse effect due to a more uniform load distribution over the bone surface.
However, such a redistribution results in some cases in that resorption of the bone tissue occurs in other places not contacting the pin, first and foremost, in the top and bottom portions of the femur which eventually results in loosening of the prosthesis. Moreover, use of osseous cement adds to labor consumption and duration of the operative procedure, as well as renders it impossible to regenerate the bone tissue at the place of application of said cement that is, makes it impossible for the pin of the endoprosthesis to accrete with its own bone tissue.